Mechanical properties of the interface between a pile and soil greatly affect the bearing capacity of a pile. The creep of soil causes a long-term strength of the pile–soil interface to be smaller than its instantaneous shear strength. It is helpful to understand the settlement deformation and strength characteristics of friction piles from the micromechanism by studying the shear creep mechanical properties of the clay–concrete interface. In this work, we carry out shear creep tests on the interfaces between clay and concrete slabs with different roughnesses under different normal stresses. We analyze the influence of the joint roughness coefficient (JRC) on the long-term cohesion and long-term friction angle of the interface. We propose an instantaneous damage factor of the shear modulus and improve the Nishihara creep model with the instantaneous damage effect of the shear modulus. The experimental results show: (1) the whole process test curve of the shear creep shows that the specimen is rapidly destroyed after the transient creep stage and the steady-state creep stage, but the tertiary creep stage is not obvious. (2) The long-term shear strength of the clay-concrete interface is greatly affected by the change in the normal stress under the same JRC conditions, and the long-term shear strength of the interface increases linearly with increasing normal stress. (3) The relationship between the long-term shear strength and normal stress of the interface can be described by the Mohr–Coulomb failure criterion, and the long-term cohesion and long-term friction angle under different JRC conditions can be calculated accordingly. There exists a critical value JRC_cr for the long-term cohesion, and the long-term cohesion of the interface first increases and then decreases as the JRC increases. When the long-term cohesion of the interface decreases to a certain extent, it fluctuates around the long-term cohesion value of clay. Moreover, the long-term friction angle of the interface fluctuates slightly with varying JRC, and there is no obvious change rule. (4) Considering the instantaneous damage of the shear modulus, we establish a relationship between the instantaneous shear modulus and the damage factor and introduce the damage factor into the Nishihara creep model. The shear creep mechanical parameters of the clay–concrete specimens under multistage loading are inversed.

桩与土壤之间的界面的机械性能极大地影响了桩的承载能力。土壤的蠕变导致桩-土界面的长期强度小于其瞬时抗剪强度。通过研究黏土-混凝土界面的剪切蠕变力学特性，有助于从微观机制了解摩擦桩的沉降变形和强度特性。在这项工作中，我们在不同法向应力下对具有不同粗糙度的粘土和混凝土板之间的界面进行了剪切蠕变试验。我们分析了接头粗糙度系数（JRC）对界面的长期内聚力和长期摩擦角的影响。我们提出了剪切模量的瞬时损伤因子，并通过剪切模量的瞬时损伤效应改进了Nishihara蠕变模型。实验结果表明：（1）剪切蠕变的全过程试验曲线表明，试样在瞬态蠕变阶段和稳态蠕变阶段后均被迅速破坏，但第三蠕变阶段并不明显。（2）在相同的JRC条件下，黏土-混凝土界面的长期抗剪强度受法向应力的变化影响很大，界面的长期抗剪强度随法向应力的增加而线性增加。（3）界面的长期抗剪强度与法向应力之间的关系可以用Mohr-Coulomb破坏准则来描述，从而可以计算出不同JRC条件下的长期内聚力和长期摩擦角。存在一个临界值JRC_cr对于长期内聚力，界面的长期内聚力首先增加，然后随着JRC的增加而减小。当界面的长期内聚力降低到一定程度时，它会在粘土的长期内聚力值附近波动。此外，界面的长期摩擦角随JRC的变化而略有波动，并且没有明显的变化规律。（4）考虑到剪切模量的瞬时损伤，我们建立了瞬时剪切模量与损伤因子之间的关系，并将损伤因子引入了Nishihara蠕变模型。在多阶段荷载作用下，黏土混凝土试件的剪切蠕变力学参数是相反的。